Reversible Gates and Testability of One Dimensional Arrays of Molecular QCA

An extensive literature exists on the mathematical characterization of reversible logic. However, the possible technological basis of this computing paradigm still remains unsolved. In this paper, quantum-dot cellular automata (QCA) is investigated for testable implementations of reversible logic. Two new reversible gates (referred to as QCA1 and QCA2) are proposed. These gates are compared (in terms of delay, area and logic synthesis) with other reversible gates (such as Toffoli and Fredkin) for QCA implementation. Due to the expected high error rates in nano-scale manufacturing, testing of nano devices, including QCA, has received considerable attention. The focus of this paper is on the testability of a one-dimensional array made of QCA reversible gates, because the bijective nature of reversible gates significantly facilitates testing of arrays. The investigation of testability relies on a fault model for molecular QCA that is based on a single missing/additional cell assumption. It is shown that C-testability of a 1D reversible QCA gate array can be guaranteed for single fault. Theory and circuit examples show that error masking can occur when multiple faults are considered.